There is quite a difference between the E90 M3 front roll bar and the E90 bar. The E90 bar tapers down in the middle and at the ends of the bar where it curves making it less rigid than the M3 bar. I've driven similar cars with the M3 front bar and OE sport bar and the M3 bar definately has less roll, but it affects ride quality a bit on bumpy roads.

I have the PS front sway bar, which is perfect for my car, and the 14mm rear bar. With 265 PSS's, PS springs and an LSD, I wish I had installed the 15mm rear bar from the E93 335i. Those PSS's stick like glue and make the rear feel a little soft when pushing it.

Most folks will probably tell you to get E90 M3 front and rear bars. I think that rear M3 bar is too stiff for a non-m. The M3 weighs a bit more, has a wider track and a much better LSD. imo, get the E90 M3 front bar and the 15mm E93 335i rear bar OR the Dinan rear roll bar.

I have the front and rear M3 bars (not sure E90/E92/etc). The rear is too stiff on the track which makes it tricky for a less experienced driver; the car will oversteer before it understeers.

We are RWD; just use the gas pedal to bring the rear around, you don't need a stiffer sway bar to reduce grip back there. Only on FWD cars does it make sense to do a stiff rear sway, they don't have many other options to help bring the rear around.

Edit: also it hasn't been mentioned, but installing the rear sway is expensive because it requires lowering the subframe + mandatory alignment. I would replace my M3 bar with the stock one if it didn't cost so much.

I want the bigger rear bar to help the car rotate during autocross. Plus I feel like the smaller (e90) m3 bar with the larger (e93) front M3 bar will help to keep the car from being overly tail happy. That, along with tc/dsc and a hell of a lot less torque than a 335i should keep the rear from stepping out too bad. In addition, the rear sport springs are a lot less stiff than the rear springs in an m3.

All told it's just a guessing game and I hate that. There's so many variables and I would definately rather rely on experience of others.

But I agree, since it is such a bitch to swap bars I would like to get it right the first time.

The Performance springs won't lower the car that much. I think cvc is on the money with the spring recommendation since you already have the Performance dampers. The stiffer springs will do more for your handling than the sways by a long shot; sways will help only in turns. Rule of thumb when upgrading a suspension is to address the main issue first and not work around it. Sways count as the latter, aka a band aid for the too-soft stock spring rates.

The Performance springs won't lower the car that much. I think cvc is on the money with the spring recommendation since you already have the Performance dampers. The stiffer springs will do more for your handling than the sways by a long shot; sways will help only in turns. Rule of thumb when upgrading a suspension is to address the main issue first and not work around it. Sways count as the latter, aka a band aid for the too-soft stock spring rates.

OP: I didn't want to lower my car either cuz I have to crawl in and out of my garage cuz I scrape the bottom of my bumper if I don't. I installed PS springs to reduce roll, squat and dive and didn't lose any clearance. Maybe 1/2" drop from zsp springs if that..
adding: labor is way more to install that rear sway bar than change springs and bumpstops. LSD swap doesn't require you to drop the rear subframe; rear sway bar does. Just a suggestion. g/l

I want the bigger rear bar to help the car rotate during autocross. Plus I feel like the smaller (e90) m3 bar with the larger (e93) front M3 bar will help to keep the car from being overly tail happy. That, along with tc/dsc and a hell of a lot less torque than a 335i should keep the rear from stepping out too bad. In addition, the rear sport springs are a lot less stiff than the rear springs in an m3.

All told it's just a guessing game and I hate that. There's so many variables and I would definately rather rely on experience of others.

But I agree, since it is such a bitch to swap bars I would like to get it right the first time.

CVC and CJ are on the $ here.

I installed PS V2 kit and am really impressed compared to ZSP. I think it is a great set-up for dd and tracking. If you notice BMW engineers did not change the rear sway bar with that kit, I am guessing they know "something" about this suspension. I would recommend that you get matched dampers and springs. The height changed only in the rear by about 1/2in, so not much. I had three instructors drive the car and they were also impressed with the V2 kit. I asked them about M3 bits and they said that is the last step after wheels/tires, brakes and lsd. I will not be installing M3 sway.

CJ, CVC - what rear toe arms would you recommend. I read there are some issues with joints with HPA parts. Meyle or other?

I installed PS V2 kit and am really impressed compared to ZSP. I think it is a great set-up for dd and tracking. If you notice BMW engineers did not change the rear sway bar with that kit, I am guessing they know "something" about this suspension. I would recommend that you get matched dampers and springs. The height changed only in the rear by about 1/2in, so not much. I had three instructors drive the car and they were also impressed with the V2 kit. I asked them about M3 bits and they said that is the last step after wheels/tires, brakes and lsd. I will not be installing M3 sway.

CJ, CVC - what rear toe arms would you recommend. I read there are some issues with joints with HPA parts. Meyle or other?